1. Field of the Invention
The present invention relates to a camera wherein lens barrels can be interchanged.
2. Description of Related Art
With this type of camera, there is a device that conveys the drive power of the drive mechanism inside the camera body (for example, a motor and deceleration gear train) to the lens barrel and drives the optical focusing system of the shooting lens in the direction of the optical axis.
With the type of camera explained above, functions realized when the lens barrel is driven by a drive mechanism inside the camera body have been limited to a single function of focussing without regard to the type of lens barrel. However, there are devices in which drive elements other than optical focussing systems (such as variable power optical systems including zoom lens systems) are built into the lens barrel. There are devices in which the drives actuators (motors), especially for zoom lens variable power movement, are incorporated into the inside of the lens barrel. Generally, variable power movement load is larger than the load for focussing. Also, in general, fixed focal length lenses are smaller than zoom lenses. Thus, the load for focussing of a fixed focal length lens is less than for a zoom lens. Thus, when fixed focal length lens focussing and zoom lens focussing are performed by an actuator installed within a camera body, the actuator is inefficient because the actuator is more powerful than necessary.